The promoter role of sulfur in carbon nanotube growth.

We investigate the effect of sulfur on the interaction of iron catalyst nanoparticles and carbon nanotubes (CNTs), typically present in a floating catalyst chemical vapor deposition (FCCVD) process. As a reference, the interaction of graphene with the Fe fcc(111) surface is used. In both systems we performed a systematic density functional theory (DFT) study on the interaction with different sulfur contents. We found that the presence of sulfur changes the nature and strength of interaction between graphene and the iron surface from strong chemisorption to weak physisorption. Furthermore, sulfur significantly reduces the CNT-iron binding, indicating a beneficial effect on the CNT growth and its promoter role. We believe that these results induce further experimental studies and optimization of the CNT synthesis process.